Field of the Invention
The present invention relates to a liquid crystal display, and more particularly to a liquid crystal display capable of improving a motion picture response time (MPRT) performance.
Discussion of the Related Art
An active matrix type liquid crystal display displays a motion picture using a thin film transistor (TFT) as a switching element. The active matrix type liquid crystal display has been implemented in televisions as well as display devices in portable information devices, office equipment, computers, etc., because of its thin profile and high definition. Accordingly, cathode ray tubes are being rapidly replaced by the active matrix type liquid crystal displays.
When a liquid crystal display displays a motion picture, a motion blur resulting in an unclear and blurry screen may appear because of the characteristics of liquid crystals. A scanning backlight driving technology was proposed so as to improve a motion picture response time (MPRT) performance. As shown in FIGS. 1 and 2, the scanning backlight driving technology provides an effect similar to an impulsive drive of a cathode ray tube by sequentially turning on and off a plurality of light sources of a backlight unit along a scanning direction of display lines of a liquid crystal display panel and thus can solve the motion blur of the liquid crystal display. In FIGS. 1 and 2, the black regions show the portions where the light sources are off and the white regions show the portions where the light sources are on. However, the scanning backlight driving technology has the following problems.
First, because the light sources of the backlight unit are turned off for a predetermined time in each frame period in the scanning backlight driving technology, the screen becomes dark. As a solution thereto, a method for controlling the turn-off time of the light sources depending on the brightness of the screen may be considered. However, in this case, the improvement effect of the MPRT performance is reduced because the turn-off time is shortened or removed in the bright screen.
Second, light interference occurs in boundary portions of the scanning blocks because turn-on times or turn-off times of the light sources of the scanning blocks are different from one another in the scanning backlight driving technology.
Third, the formation location of the light sources of the backlight unit are limited because the scanning backlight driving technology can be successfully implemented by controlling light incident on the liquid crystal display panel in each of the scanning blocks. The backlight unit may be classified into a direct type backlight unit and an edge type backlight unit.
In the direct type backlight unit, a plurality of optical sheets and a diffusion plate are stacked under the liquid crystal display panel, and a plurality of light sources are positioned under the diffusion plate. Thus, it is easy to achieve the scanning backlight driving technology in the direct type backlight unit having the above-described structure.
On the other hand, in the edge type backlight unit, a plurality of light sources are positioned opposite the side of a light guide plate, and a plurality of optical sheets are positioned between the liquid crystal display panel and the light guide plate. In the edge type backlight unit, the light sources irradiate light onto one side of the light guide plate and the light guide plate has a structure capable of converting a line light source (or a point light source) into a surface light source. In other words, the characteristics of the light guide plate are such that the light irradiated onto one side of the light guide plate spreads on all sides of the light guide plate. Therefore, it is difficult to control light incident on the liquid crystal display panel in each of the display blocks and hence, it is difficult to achieve the scanning backlight driving technology in the edge type backlight unit having the above-described structure.